1. Field of the Invention
The present invention relates generally to magnetic tape cassettes and more particularly to a magnetic tape cassette suitable for use in recording a digital signal such as a PCM (pulse code modulated) signal.
2. Description of the Prior Art
A PCM recording and/or reproducing apparatus has been previously proposed for recording an analog audio signal on a magnetic tape or reproducing the same therefrom in the form of a digital signal such as a PCM signal. The known PCM recording and/or reproducing apparatus employs a rotary head to provide a recording in which the PCM signal is recorded with relatively high density. In the PCM recording and/or reproducing apparatus using the rotary head, upon recording and/or reproduction, the magnetic tape is withdrawn from a magnetic tape cassette and wrapped around a rotary drum on which the rotary head is mounted. The recording and/or reproducing is performed under this state.
In a magnetic tape cassette in which a magnetic tape of the type described above is incorporated, when the magnetic tape is smudged with fingerprints, oily compounds, dust or the like, a drop-out occurs in the reproduced signal. Therefore, the magnetic tape has to be sealed as tightly as possible so that it can be protected from fingerprints, dust, smudges and the like.
A magnetic tape cassette shown in FIGS. 1 to 5 has previously been proposed for such a purpose. FIG. 1, which is a perspective view of the conventional magnetic tape cassette, shows a cassette housing represented by reference numeral 1. This cassette housing 1 comprises an upper half or part 2 and a lower half or part 3, which are secured together by suitable conventional means such as screws (not shown). A transparent window plate 2a is provided integrally on the top surface of the upper part 2 so that the amounts of tape wound on each reel can be visually confirmed. Within the cassette housing 1, a pair of reel hubs 4 are rotatably inserted into a pair of reel shaft insertion apertures 5 (refer to FIG. 2) that are formed in the lower part 3 at respectively predetermined positions. A magnetic tape 6 is wound around the pair of reel hubs 4.
FIG. 2, which is a perspective, exploded view of the conventional tape cassette of FIG. 1, shows upper and lower inserts 6a, 6b made of a material having a low coefficient of sliding friction with the magnetic tape 6 and respectively having guiding ribs 6c, 6d serving the purpose of ensuring that the magnetic tape 6 is wound smoothly and evenly on the reel hubs 4. The ribs 6c of the upper insert 6a are convex downwards (towards the magnetic tape), and the ribs 6d of the lower insert 6b are convex upwards (also towards magnetic tape 6).
FIG. 2 also shows tape guide posts 7 that are formed on the lower part 3 at its front portion, one of the guide posts 7 being at a position near the right side wall of the lower part 3 and the other of the guide posts 7 being at a position near the left side wall of the lower part 3. The magnetic tape 6 is guided by the tape guide posts 7 so that it can be transported along a predetermined path at the front portion of the cassette housing. A cut-away recess portion 3a of a substantially rectangular configuration having a predetermined width is formed on the lower part 3 in such a manner as to oppose the rear side of the magnetic tape 6 guided between the tape guide posts 7. Upon recording or reproduction, a magnetic tape withdrawing guide system of a recording and/or reproducing apparatus (not shown) is inserted into this cut-away recess portion 3a in order to withdraw the magnetic tape 6 so that it can be wrapped around the rotary drum as explained above.
A front lid 8 is rotatably supported on the front portion of the cassette housing 1 by right and left arm portions 8a of the lid 8 so as to open and/or close the front of the cassette housing 1 in which the magnetic tape 6 is contained. When the tape cassette is not in use, the front lid 8 closes the front portion of the cassette housing 1 so that the cassette housing 1 completely encloses and protects the magnetic tape 6.
A slidable plate member or slider 9 is mounted on the lower surface side of the lower part 3 of the cassette housing 1 so as to move slidably in the front to back direction (from left to right in FIGS. 3 and 4). As FIG. 2 shows, apertures 10 corresponding to the reel shaft insertion apertures 5 are formed in the bottom portion of the slider 9 so that the apertures 10 communicate with the apertures 5 when the slider 9 is slidably moved backward so as to open the recess portion 3a of the lower part 3. Two pairs of apertures 12a, 12b are formed in the bottom portion of the slider 9 at its front right and left sides with a predetermined spacing therebetween. These apertures 12a, 12b are elastically engageable with a pair of right and left slide plate locking members 11 provided on the bottom portion of the lower part 3 when the slider 9 is slidably moved to its forwardmost position or its rearmost position.
A pin 13 is centrally implanted on the bottom portion of the slider 9 at its front end. This pin 13 is engaged with a torsion spring 14 at its coil portion. One end portion of the torsion spring 14 is engaged with the front wall 3b of the lower part 3 and the other end portion thereof is engaged with the front edge of the slider 9 so that the slider 9 is spring-biased by the torsion spring 14 in such a manner that it is always urged to slide forward.
When the tape cassette is being stored and in general when it is not being used, the slider 9 is placed in its forwardmost position to close the recess portion 3a and the reel shaft insertion apertures 5 of the cassette housing 1 as shown in a side view forming FIG. 3. Under this condition, the slider locking members 11 are engaged in the rear engaging apertures 12a to keep the slider 9 in the position in which it closes the recess portion 3a and the apertures 5 of the cassette housing 1. When the tape cassette is loaded into the magnetic recording and/or reproducing apparatus (not shown), the mechanism of the magnetic recording and/or reproducing apparatus releases the slider locking members 11 from the rear engaging apertures 12a, and the slider 9 is slidably moved backward (or towards the right in FIG. 3) against the spring force of the torsion spring 14 to expose the recess portion 3a and the reel shaft insertion apertures 5 of the cassette housing 1. Under this condition, the slider locking members 11 are engaged in the front engaging apertures 12b to keep the slider 9 in its opened state (FIG. 4).
FIGS. 2 to 4 show a pair of limiter pins 15 formed on the inner surface of the upper part 2 at positions that respectively correspond to the positions of the left and right slide plate locking members 11 of the lower part 3. The lower ends of the limiter pins 15 are respectively opposed to the top surfaces of the slider locking members 11 with a predetermined spacing as shown in FIGS. 3 and 4. Thus, when the slider locking members 11 are warped inwardly too much, the lower ends of the limiter pins 15 come in contact with the slider locking members 11 to prevent the slider locking members 11 from being broken or excessively deformed.
On the inside of the upper and lower parts 2 and 3 of the cassette housing 1, there is provided a reel braking member 16 that prevents the tape reels 4 from being inadvertently or unintentionally rotated by shock and so on (FIG. 2) and therefore prevents the magnetic tape 6 from becoming slack.
As FIG. 2 shows, this reel braking member 16 is mainly formed of an upper surface supporting plate portion 16a extending along the inner surface of the upper part 2 and left and right leg plate portions 16b elongated downwardly from both end portions of the upper surface supporting plate portion 16a so that the reel braking member 16 has a cross section substantially in the shape of the letter U. The upper surface supporting plate 16a has formed on its rear edge a pair of braking protrusions 16c corresponding to ratchet wheel portions 4a formed around both of the reel hubs 4. The lower ends of the leg portions 16b are extended forward to form operation members 16d at their ends.
A spring 17 is attached to the upper surface supporting portion 16a of the braking member 16 at its central portion. This spring 17 has its ends extended so that it has substantially the shape of the letter V, and these ends of the spring 17 are brought into contact with and bear against the rear surface of the front wall of the upper part 2.
When the tape cassette is not in use, and in general whenever the front lid 8 is closed, the braking member 16 is slid backward by the force of the spring 17 so that the protrusions 16c engage with the ratchet wheels 4a of the reel hubs 4 as shown in FIG. 3 and the reel hubs 4 are prevented from rotating. When the front lid 8 is opened by upward rotation (clockwise rotation is moving from the position shown in FIG. 3 to that shown in FIG. 4), the ends of the arm portions 8a of the front lid 8 press the operation members 16d of the reel braking member 16 so that the reel braking member 16 is slidably moved forward against the spring-biasing force of the spring 17 to release the protrusions 16c from the ratchet wheels 4a of the reel hubs 4, thus allowing the reel hubs 4 to rotate as shown in FIG. 4.
When a magnetic tape cassette having the braking member 16 is assembled in the conventional manner, the magnetic tape 6 wrapped around the reel hubs 4 is first assembled on the lower part 3 and then the braking member 16 is assembled. In this assembly process, however, the presence of the spring 17 is so disturbing that the braking member 16 cannot be assembled at the predetermined position without difficulty. Also, while the lower part 3 on which the magnetic tape 6 and the braking member 16 are temporarily assembled is being conveyed on the assembly line, the braking member 16 frequently comes out of the lower part 3.
To avoid this problem, it has been recently proposed to modify this kind of magnetic tape cassette so that, during the assembly, a braking member is temporarily assembled on the upper part beforehand in the manner disclosed in Japanese laid-open utility model Gazette No. 62-39283.
This previously-proposed tape cassette is illustrated in FIG. 5, which is a fragmentary, cut-away side view of the upper part 2 in an inverted position. As FIG. 5 shows, openings 18 of rectangular configuration are formed in left and right portions of the upper supporting plate portion 16a of the braking member 16 along the direction in which the braking member 16 is slidably moved. The length of each of the rectangular openings 18 is equal to the length of the stroke made by the braking member 16 when it is engaged with or disengaged from the reel hubs 4. In correspondence with the rectangular openings 18, caulking pins 19 are formed monolithically on the lower surface of the upper part 2 and respectively inserted in the rectangular openings 18 of the braking member 16. Under this condition, the top portions (as shown in FIG. 5) of these caulking pins 9 are melted by ultrasonic welding or the like to form head portions 19a whereby the braking member 16 is slidably supported on the upper part 2.
In the temporary assembly of the braking member in this prior art magnetic tape cassette, a somewhat complicated process is required to caulk the caulking pins 19. Also, depending upon the caulking conditions and so on, a so-called sagging sometimes occurs below the neck portions of the head portions 19a of the caulking pins 19, and this sagging frequently modifies the rectangular openings 18 of the braking member 16 in a manner that is deleterious to the operation of the braking member 16. In particular, after the magnetic tape cassette is fully assembled, upon use, the braking member 16 cannot be operated smoothly and cannot follow the opening and/or closing operation of the front lid 8 so that the reel hubs 4 cannot be locked positively, thereby allowing slackening of the magnetic tape 6. Moreover, when such a magnetic tape cassette is loaded into the recording and/or reproducing apparatus, jamming or mis-loading sometimes occurs.